1. Field of the Invention
The present invention relates to an ink, and an ink-jet recording method and instruments making use of the ink. In particular, it relates to an ink which can provide images excellent in water fastness on non-coated paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and continuous business forms, i.e., so-called plain paper, which are commonly used in offices and homes, and is excellent in solution stability and suitable for use in a system capable of high-image quality recording using bubble-jet printer, and an ink-jet recording method and instruments making use of such an ink.
The present invention also relates to an ink-jet recording ink, and particularly to an ink which can provide images excellent in water fastness on all recording materials, in particular, non-coated paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and continuous business forms, i.e., so-called plain paper, which are commonly used in offices and homes, has an ideal black color, and is excellent in solution stability and suitable for use in a system capable of high-image quality recording using bubble-jet printer, and a recording method and instruments making use of such an ink.
Further, this invention relates to an ink capable of conducting recording free of feathering and unevenness of color strength on plain paper, and an ink-jet recording method making use of such an ink.
Still further, the present invention relates to a method of preventing the association of a dye.
Yet still further, the present invention relates to a liquid composition that is not corrosive to metal, by which the corrosion of a metal caused by a liquid kept in contact with the metal can be effectively prevented, for the purpose of enhancing the reliability of various apparatus and instruments of a structure that their metal surfaces are brought into contact with the liquid upon their use. In particular, the present invention relates to a liquid composition and an ink that are not corrosive to metal, by which in apparatus suitable for use in non-impact recording, especially, apparatus in which ink droplets are ejected to conduct recording, such as copying machines, facsimile terminal equipments, word processors, printers and plotter, the corrosion of metal parts such as heating resistors and electric conductors installed in these apparatus, which may be caused by their direct contact with ink upon their use, can be effectively prevented, and an ink-jet recording method making use of such an ink.
2. Related Background Art
Inks with greatly various manners of being composed have been hitherto reported in respect of inks for ink-jet recording. In particular, in recent years, detailed researches and developments have been made from various aspects such as compositions and physical properties of inks because of a demand for improving the water fastness of images upon recording on plain paper such as paper for copying, paper for reporting, notepaper, letter paper, bond paper and continuous business forms, which are commonly used in offices.
For example, Japanese Patent Application Laid-Open Nos. 2-296878 and 2-255876 have proposed to contain a polyamine in a water-based ink composition.
In such an ink, however, the polyamine forms a salt with a hydrophilic group in a dye contained in the ink, and so the solution stability of the ink is lowered. Therefore, there are potential problems of reduction in reliability such as clogging at the tip of an orifice, and of bronzing (association of the dye) on a recording material, which may result in unevenness of printing and/or low density. It has also been considered to contain a dissolution stabilizer in the ink for a purpose of improving the solution stability of the ink. In this case, however, it is necessary to contain a great amount of the dissolution stabilizer in the ink, so that the image quality of prints formed with such an ink becomes deteriorated.
Besides, Japanese Patent Application Laid-Open No. 3-91577 has proposed to improve the water fastness of images by providing a dye having at least one carboxyl group in which the carboxyl group is formed into an ammonium salt or a volatile substituted ammonium salt, whereby ammonia or amine vaporizes on a recorded article to form a free acid.
Even in this case, however, ammonia or amine gradually vaporizes in the ink, and so the solubility of the dye is lowered, which may often form the cause of clogging at an orifice and reduction in stability of the ink though the initial solubility of the ink is good. For the same reason, bronzing tends to occur on a recording material, in particular, on acid paper.
The color tone of the dye described in Japanese Patent Application Laid-Open No. 3-91577 is somewhat royal-purplish, and a problem of the color tone hence remains unsolved.
Such a problem of color tone have had importance with the advance of color recording. More specifically, when black-color printing is conducted, it is of course ideal for a black ink to have a black color near a primary color as much as possible. Further, full-color printing requires for attaining ideal color reproduction well-balanced that in addition to magenta, yellow and cyan inks, a black ink should produce a color near a primary color. Besides, EP 0468647 A1, EP 0468648 A1 and EP 0468649 A1 describe disazo dyes and phthalocyanine dyes having at least one carboxyl group.
Further, U.S. Pat. No. 4,963,189 describes disazo dyes having at least one carboxyl group.
However, these dyes are originally hard to be dissolved in water, so that the water fastness of prints formed from an ink containing such a dye is improved compared with the conventionally-used inks. However, these dyes tend to cause a disadvantage that when such a dye is dissolved in water or a solvent to prepare an ink, the water or solvent evaporates where a cartridge containing the ink is left over for a long period of time, for example, so that the ink becomes highly viscous, dried and lastly solidified, resulting in failure of printing (such a condition will hereinafter be called "crusting"). Similarly, they may cause a disadvantage that stable ejection of the ink cannot be conducted during printing, or in the case where after the ink is ejected from an orifice, the ejection of the ink is suspended for a certain period of time (for example, 1 minute) and a first droplet of the ink is then ejected from that orifice, resulting in uneven printing (such a condition will hereinafter be called "poor first-ejection").
U.S. Pat. No. 4,963,189, 5,062893 and 5,062,892 disclose techniques of reducing kogation, i.e. a phenomenon that some components of ink are thermally decomposed and built up on a heater element of an ink-jet head and of adding 0.2% by weight (0.02 mol/l, 0.58 mol/mol of dye) of sodium phosphate as a pH buffer to an ink. They also disclose a technique of adding an oxo anion to reduce the kogation on the heater.
The above techniques cannot provide images free of unevenness of color strength and satisfactory in print density.
With respect to recording apparatus, those of very various systems have heretofore been reported. For example, Japanese Patent Application Laid-Open No. 58-36465 discloses an ink On-Demand printing system making use of ink-containing capillary tubes having orifices through which an ink is ejected.
In such an ink On-Demand printing system, an ink-heating element is arranged in close vicinity to each of the orifices. For this reason, each ink-containing capillary tube or a heating resistor provided in the vicinity thereof is rapidly heated, and moreover transfers a large amount of thermal energy to the ink in close vicinity to the orifice, whereby a minute part of the ink is vaporized to generate bubbles in the capillary tube. In consequence, the bubbles generate a pressure wave by which an ink droplet is ejected out of the orifice on the surface of a recording material. If the position of the ink-heating element to the orifice is suitably preset, and the transfer of energy from the heating element to the ink is carefully controlled, the bubbles vanish on the ink-heating element or in the vicinity thereof before the vapor escapes from the orifice.
The service life of such a thermal ink-jet printer is known to depend on, in particular, the service lives of an electric conductor and a heating resistor. Remarkable troubles arising on such electric conductor and heating resistor are caused by cavitation damage due to vanishing of bubbles and chemical damage by ink. Therefore, in order to elongate the service life of the thermal ink-jet printer, it is desirable to prevent the fatigue of the heating resistor due to chemical change and check the damage due to the occurrence of cavitation to the minimum.
In this regard, for example, Japanese patent Application Laid-Open No. 59-109372 discloses a solution for reducing the fatigue of a heating resistor. More specifically, a heating resistor is generally covered with an inert layer for protecting it against chemical fatigue and mechanical fatigue during its operation. In this publication, a thin layer of silicon carbide, silicon oxide or aluminum oxide is disclosed as the inert layer.
Japanese patent Application Laid-Open No. 59-95157 also discloses the use of silicon-oxynitride, aluminum oxide or titanium oxide in addition to silicon dioxide as an inert layer or a protective layer, in which a layer is first formed on a orifice plate, and a heating resistor and an electric conductor are covered with these inert layers.
Further, Japanese Patent Application Laid-Open No. 58-221341 discloses that a similar inert layer formed of silicon dioxide or silicon carbide is coated on a heating resistor (tantalum/aluminum alloy) and a electric conductor (aluminum), both, formed in advance.
Moreover, Japanese patent Application Laid-Open No. 59-100214 discloses a structure of an inert layer composed of two layers of silicon carbide and silicon nitride or silicon oxide.
In each of the publications, the surface protection of the heating resistor and the like making use of the inert substances as described above has been fully satisfactory as to the fatigue properties.
However, if cracks and/or pinholes exist in the inert layer or surface-protective layer composed of the inert substance and provided on the heating resistor, the surface-protective layer has involved a problem that it cannot exhibit the desired properties. In particular, if the surface-protective layer is in contact with a liquid (for example, an ink), the ink comes into contact with the heating resistor through these cracks and/or pinholes, so that a metal making up the heating resistor is corroded by the ink, resulting in electrical disconnection of the resistor. As a result, heat is not transferred to the ink, and so a uniform size of ink droplets cannot be ejected out of an ink-jet head at an even rate and in a fixed orbit.
On the other hand, it is difficult to completely do away with the cracks and pinholes in the surface-protective layer in a practical production process of the heating resistors. There is hence a demand for early solving the above problem.
Furthermore, U.S. Pat. No. 5,062,892 also discloses inks for thermal ink-jet, which contain an oxo anion such as a phosphate, a sulfate or an oxalate. Such inks involve a problem that they dissolve surface-protective layers provided on an electric conductor and a heating resistor and cause chemical damage due to kogation, resulting in failure in ejection of ink.